198 SPECIAL SENSES. 



ward, and may be increased or diminished by the action of 

 the muscles of the middle ear. The point of greatest con- 

 cavity, where the extremity of the handle of the malleus is 

 attached, is called the umbo. Yon Troltsch has described, 

 upon the inner surface of the membrane, two pouches, or 

 pockets. One is formed by a small, irregular, triangular fold 

 situated at the upper part of its posterior half, and consisting 

 of a process of the fibrous layer. This, which is called the 

 posterior pocket, is open below, and ex'tends from the poste- 

 rior upper border of the membrane to the handle of the mal- 

 leus, which it assists in holding in position. " After it has 

 been divided, this bone is much more movable than before." 

 The anterior pocket is lower and shorter than the posterior. 

 It is formed by a small bony process turned toward the neck 

 of the malleus, by the mucous membrane, by the bony pro- 

 cess of the malleus, by its anterior ligament, the chorda tym- 

 pani, and the anterior tympanic artery. 1 The handle of the 

 malleus is inserted between the two layers of the fibrous 

 structure of the membrana tympani and occupies the upper 

 half of its vertical diameter, extending from the periphery 

 to the umbo. 



The membrana tympani, though thin and translucent, 

 presents three distinct layers. Its outer layer is an exces- 

 sively delicate prolongation of the integument lining the ex- 

 ternal meatus, presenting, however, neither papillae nor glands. 

 The inner layer is a delicate continuation of the mucous mem- 

 brane lining the tympanic cavity, and is covered by tessel- 

 lated epithelial cells. The fibrous portion, or lamina propria, 

 is formed of two layers. The outer layer consists of fibres, 

 radiating from the handle of the malleus to the periphery. 

 These are best seen near the centre. The inner layer is coin- 

 posed of circular fibres, which are most abundant near the 

 periphery, and diminish in number toward the centre. Be- 

 tween these two layers, are fusiform corpuscles, described 

 first by Yon Troltsch, 2 which resemble the corneal corpuscles. 



1 TROLTSCH, Diseases of the Ear, New York, 1869, p. 32. 2 Loc. cit. 



